Felix Fietkau has turned of the diagnostics for
STA txq pending airtime underflow:
and he works/worked for/with MediaTek, example with its copyrights is below:
but the "STA txq pending airtime underflow" still wasn't fixed and when it happens the only solution is to reboot the router... (otherwise it scrambles the traffic, decreases the speed and so on)
Can somebody explain what is going on?